692779 - Zooming out breaks some layouts

Status: RESOLVED WONTFIX

(Core :: Layout, defect)

Description

[Albert Juhé]

Attachment: example.htm

See example.htm:

We have a wrapping div (gray) with a width of 304px. Inside it there are two other div (red and green) floating left with a width of 150px and a border of 1px.

In normal zoom you cannot see the wrapping div, it's OK. But if you zoom out (Ctrl -) the two divs inside the wrapper appear one over the other and you can see the gray div.

It think that it should not happen: in many cases this breaks the page layout.

Furthermore:
It does not happen if you use "-moz-box-sizing: border-box" in the inside divs. (see example2.htm)

Comment 1

[Albert Juhé]

Attachment: example2.htm

Comment 2

[Boris Zbarsky [:bzbarsky]]

This is presumably happening because borders are snapped to device pixels, right?  So if you zoom out a little bit, the 304 and 150 get smaller in device pixels but the 1 does not, and then things no longer fit...

Comment 3

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Right. This is more or less by design and I don't want to change anything here. The alternatives would make border edges get inconsistent widths (possibly disappearing completely), or else getting nasty antialiasing.

If you know what rendering you want at, say, a zoom of 1.2, you can tweak the CSS to get that. Basically one of the inner elements is going to have to have an auto width.